Dodge: The Genus Gymnosporangium 



187 



general features of small portions at the center of young sori. 

 Various stages in the degeneration of the terminal cells will be 

 described in connection with the discussion of the next species, 

 where the conditions are practically the same. 



Gymnosporangium globosum 



The best material was obtained at Cold Spring Harbor, No- 

 vember 30. The location of the primordia could not be deter- 

 mined definitely on this date, as the sori had not even begun to 

 form. The rust was therefore allowed to develop further in the 

 greenhouse until December 16. The young sori could then be 

 located by the appearance of mound-like swellings over which the 

 cork layer was tightly stretched. The covering was as yet un- 

 broken. Sections of such a swelling showed a broadly elliptical 

 sorus primordium, at the center of which teleutospore buds were 

 plainly visible. Sori began to break through the surface about 

 ten days later and by the middle of January the large telia had 

 developed quite normally. 



The cork layer covering the galls is somewhat thicker than we 

 find in the galls caused by G. macro pus. There are usually five 

 to eight layers of irregular cork cells and the outer ones may be 

 more strongly suberized. The parenchyma cells are well supplied 

 with starch, and haustoria are present, although not in consid- 

 erable numbers. There is usually a single nucleus in each haus- 

 torium. The earlier stages in the formation of the sorus are sim- 

 ilar to those described in connection with the preceding species. 

 There is a more pronounced massing of the hyphae and the 

 pseudo-parenchyma is more compact (Plate 10, Fig. 5). 



In G. globosum the development of the sorus is evenly pro- 

 gressive. At the margin the hyphae are crowded in between the 

 outer parenchyma cells, lifting up the cork layer slightly. Further 

 in the pseudoparenchyma is well formed with terminal cells 

 pushed up squarely against the cork layer. Figures 9 and 10 in 

 plate 11 were drawn from different portions of a section through 

 a sorus. Figure 9 shows the condition at the margin, which is 

 abnormally high in this section, due to an irregularity in the gall. 

 Figure 10 represents a more mature condition toward the center. 



